lookup-module-by-name

Arguments:
system-or-mg module-name &optional errorp

This function looks for a module named
module-name in the system or module-group
module-container specified by the first argument. First the modules
list of the module-container is searched for a module of the given
name. If not found, then the search continues recursively by calling
lookup-module-by-name
with the parent-object
of the module-container. If no module named
module-name is found then nil is returned (if errorp has
its default value of nil) or an error is
signaled (if errorp is specified
true). If the module is found, then the module is
returned.

See defsystem.htm
for general information on the Defsystem facility in Allegro CL.